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Thanks to Dr. Julia
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Case of the Week
#175

Clinical
History

A 70 year old woman presented with
confusion, lethargy, short term memory loss, disorientation, and fever. She
had a history of CNS vasculitis and a right thalamic CVA.

MRI showed a rounded lesion in the
right cerebral peduncle and the right putamen / inferior lateral thalamus.
Radiologically it was a homogeneous lesion with slight effacement of the right
lateral ventricle. The radiologic differential diagnosis was lymphoma, primary
glial neoplasm or subacute infarct. There was no other significant medical
history.

A biopsy was obtained.

MRI image:

Micro images:

Smear preparation

Permanent section

Stains:

H&E and
reticulin

CD20 CD3

EBER (in situ
hybridization stain for EBV encoded RNA)

MIB-1

What is your diagnosis?

Diagnosis:

Primary diffuse large B cell lymphoma
of the CNS

Discussion:

Primary diffuse large B-cell
lymphoma of the central nervous system is a rare tumor that by definition, arises exclusively in the CNS with no obvious
lymphoma elsewhere at diagnosis. It represents 5-10% of CNS neoplasms in
patients ages 75+ (Hum
Path 2003;34:1137). A majority of these neoplasms arise supratentorially
within the white matter and in the periventricular area. They may be
multifocal and may affect the leptomeninges, but primary leptomeningeal
involvement is rare. At diagnosis, 20% have ocular involvement; and 80-90% of
these patients develop contralateral tumors and intraparenchymal CNS lesions,
with invasion of the subretinal pigment epithelial space and vitreous.
Dissemination to extraneural sites such as bone marrow is extremely rare.

Radiologically, these tumors are
generally solitary, homogeneously contrast enhancing and usually have no ring
enhancement, in contrast to glioblastoma multiforme and metastases.

Grossly, most central lymphomas are
solid, grey, ill-defined, and usually deep-seated. Some travel along white
matter tracts and transcend the corpus callosum, like infiltrating gliomas. Histologically,
they are widely infiltrating with a perivascular predilection. Most are
discohesive, but may occur in a glial meshwork within the CNS. Primary brain
lymphomas have scant cytoplasm, high grade nuclei and multiple nucleoli, but
less pleomorphism than other high grade CNS tumors. Most primary CNS lymphomas
are diffuse large B cell subtype, and are immunoreactive for CD20, CD79a and
CD22, but negative for CD3. However, nearly all tumors have a background of reactive
T cells that may lead to an erroneous diagnosis of T cell lymphoma. The
mitotic index is often > 50%.